Colored anodizing is very difficult to match lot to lot, never mind part to part, or specific alloy to specific alloy. bars, stems and posts may be made of slightly different materials, or processes, or have different surface properties, and will respond differently to the anodizing process.

Forged parts with their harder tighter surfaces tend to come up brighter than parts made from extrusion or castings, which in turn will be different from a part machined from billet.

It's just that way things are, and if you're that finicky about color stick to silver and black, though even those don't always match perfectly.

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